Heat a waffle iron to high, according to manufacturer's instructions.
Whisk together buckwheat flour, oat flour, ground flaxseed, baking powder, baking soda, cinnamon, salt, cardamom (if using), and nutmeg in a large bowl.
In a separate bowl, whisk together buttermilk, egg, egg white, coconut oil, maple syrup, and vanilla; stir into flour mixture just until combined. Let sit 5 minutes.
Ladle about a third of a cup of batter onto each waffle section, close iron and cook until waffles are crispy. This will take about double the time of most waffle recipes, I found 10 minutes to be perfect. Start checking at about 6 minutes, as waffle irons vary.
Repeat with remaining batter. Serve with fresh strawberries and pure maple syrup, or desired toppings.